1. Technical Field
The present invention generally relates to a probe for ultrasonic flaw detectors, and more particularly to a probe having an allowable service temperature limit greatly extended both in the high temperature and in the low temperature directions.
2. Background Art
Recently, along with the general trend of prolonging the service lifetime of various types of structures, the need to measure the degree of aging of such structures is increasing. Ultrasonic apparatus offers an effective means of assessing the remaining lifetime of these structures, in terms of the fatigue of the structure.
The conventional normal scan probe or a straight beam testing probe for such an ultrasonic apparatus is exemplified in FIG. 5 of the accompanying drawings, where the probe b is in slidable contact with the object or structure a to be tested, through a couplant, such as, for example, water or glycerol. The probe b is constructed by bonding a transducer f, which is made from an oscillator crystal, such as Pb(Zr, Ti)O.sub.3, and which is sandwiched between a pair of electrodes e made by baking silver thereon at a low temperature of about 300 degrees C., onto a ceramic protection plate d, which comes in contact with the structure being tested through couplant c, with an epoxy type resin adhesive g.
The type of probe b, described above, is undesirable in that, when the structure a is one which may be heated to a high temperature, such as a nuclear reactor pressure vessel, the adhesive g is liable to separate under thermal expansion of the ceramic protection plate d, thereby limiting the allowable service temperature of the probe b to 150-200 degrees C., and restricting the application to those objects which will not become too hot.
When the structure is one which may become too cold, on the other hand, separation of adhesive g is also liable to occur upon contraction of the ceramic protection plate d, thus limiting cold temperature applications.